As a material for forming a resist underlayer film for EUV exposure, a resist underlayer film forming composition that reduces generation of outgas is disclosed (Patent Document 1). As another disclosure, a resist underlayer film forming composition including a reaction product of a bifunctional diglycidyl ester compound and 2,4-dihydroxybenzoic acid, which is not specified as a material for EUV exposure, is also disclosed (Patent Document 2). However, in Patent Document 1 and Patent Document 2, a two-dimensional polymer obtained by a polyaddition reaction of a bifunctional diglycidyl ester compound and bisphenol S or its derivative is not disclosed and not suggested.